Monofunctional ether heat and mass transfer additives for aqueous absorption fluids

ABSTRACT

An aqueous absorption fluid composition, process and apparatus wherein the absorption fluid contains at least one monofunctional ether heat and mass transfer additive which provides improved water vapor absorption and thermal transfer in thermal exchange loops used in absorption refrigeration, chilling, heat pump, energy storage and other thermal transfer applications.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part application of application, U.S. Ser. No. 09/280,787, filed on Mar. 26, 1999 now U.S. Pat. No. 6,187,220. The co-pending parent application is hereby incorporated by reference herein and is made a part hereof, including but not limited to those portions which specifically appear hereinafter.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an aqueous absorption fluid composition, process and apparatus providing improved water vapor absorption and thermal transfer. Addition of small quantities of certain ethers to an aqueous absorption fluid composition provides improved heat and mass transfer resulting in improved water vapor absorption and enhanced thermal and chemical stability. The compositions of this invention are particularly suited for use in high temperature stages of thermal transfer loops used in absorption refrigeration, chilling, heat pump, energy storage and other thermal transferring applications.

2. Description of Related Art

Aqueous metal halide solutions are well known as refrigerant/absorbent solutions for absorption refrigeration systems as taught by U.S. Pat. No. 3,478,530.

Alcohols have been widely used as additives in small amounts to aqueous refrigerant absorbent solutions for improved heat transfer. Octyl alcohol in LiBr solutions is taught by U.S. Pat. Nos. 3,276,217 and 4,857,222; certain secondary alcohols in LiBr solutions are taught by U.S. Pat. Nos. 3,609,087 and 4,315,411; certain tertiary alcohols are taught by U.S. Pat. No. 3,580,759; and fluoroalcohols are taught by U.S. Pat. No. 3,783,631.

Amines have been used as additives in small amounts to aqueous absorption systems for increased rate of water vapor sorption of working fluid as taught by U.S. Pat. Nos. 5,419,145; 5,577,388 and 5,829,259, for example.

Certain ethers are known as solvents for refrigerant methyl chloride used in absorption refrigeration as taught by U.S. Pat. No. 2,040,905.

The polyfunctional ethers, ethylene glycol monobutyl ether and diethylene glycol monobutyl ether, in amounts of 0.001 to 1.0 percent by weight, in concentrated lithium halide aqueous solutions are known as vapor pressure depressants for use in absorption refrigeration systems, as taught by U.S. Pat. No. 3,553,136.

The use of polyfunctional ether, specifically tetraethylene glycol dimethylether, as an absorbent in conjunction with an azeotropic mixture of trifluoroethanol and water as a cooling medium is taught by Japanese Patent Number 61-14282 to afford a wider temperature range of a cycle than a water/LiBr system in absorption refrigeration.

An absorption fluid of aqueous solutions of metal salts of alkali metal hydroxides, nitrites, and alkaline earth and transition metal hydroxides, halides and thiocyanates and about 10 to about 30 weight percent, based on the metal salt, of an organic compound including ethers, particularly alkaline glycol ethers is taught by U.S. Pat. No. 5,529,709 to provide increased absorbent solubility and vapor pressure reduction.

SUMMARY OF THE INVENTION

It is an object of this invention to provide an improved aqueous absorption fluid composition and process for thermal transfer having increased rates of water vapor absorption to result in improved thermal transfer.

It is another object of this invention to provide an improved aqueous absorption fluid composition and process for thermal transfer which allows use of reduced absorber size to obtain a specified thermal transfer.

Yet another object of this invention is to provide an aqueous absorption fluid composition which exhibits high stability to thermal decomposition and chemical reactivity to other components of the composition.

In particular, the general object of the invention can be attained, at least in part and in accordance with one embodiment of the invention, through an absorption fluid composition which includes aqueous refrigerant, at least one metal halide salt absorbent present in an amount to provide a composition useful as a refrigerant/absorbent and at least one monofunctional ether heat and mass transfer additive normally liquid at system operating conditions and present in an amount effective as an absorption promoter.

The invention further comprehends an improvement in a process for thermal transfer using an absorption fluid which includes an aqueous metal halide salt refrigerant/absorbent composition. In accordance with one embodiment of such invention, such improvement relates to obtaining an increased rate of water vapor absorption in the absorption fluid via adding thereto an absorption promoting amount of at least one monofunctional ether heat and mass transfer additive normally liquid at system operating conditions.

The invention still further comprehends an improved apparatus for absorption thermal storage, cooling or heating of the type containing an absorption fluid which includes aqueous refrigerant and at least one metal halide salt absorbent present in an amount to provide a composition useful as a refrigerant/absorbent. In accordance with one preferred embodiment, such improvement relates to the absorption fluid additionally including an absorption promoting amount of at least one monofunctional ether heat and mass transfer additive normally liquid at system operating conditions.

The above objects and other advantages of this invention which will become apparent upon reading this disclosure are achieved by addition of parts per million amounts of certain ethers to aqueous absorption fluids.

As used herein, references to “monofunctional” ether heat and mass transfer additives are to be understood to refer to such ether additives that contain or include only a single organic functional group, i.e., a single ether chemical group. The term “organic functional group” is not meant to include aliphatic and aromatic hydrocarbon groups such as phenyl, butyl, hexyl and the like. It is to be understood, however, that a monofunctional ether as used herein may, in certain preferred embodiments, be at least partially fluorinated such as to contain one or more fluorine groups.

Further, references herein to “polyfunctional” ether or other additive material are to be understood to refer to such an additive material which contains or includes two or more organic functional groups, wherein the two or more organic functional groups can be of the same or different type. Examples of polyfunctional additives include: ethylene glycol (i.e., contains or includes two alcohol functional groups), diethylene glycol (ether) (i.e., contains or includes one ether and two alcohol functional groups), ethylene glycol monobutyl ether (i.e., contains or includes one ether and one alcohol functional group), diethylene glycol dibutyl ether, (i.e., contains or includes three ether functional groups), diethylene glycol monobutyl ether acetate (i.e., contains or includes two ether and one ester functional groups), and monophenyl glycol ether acetate (i.e., contains or includes one ether and one ester functional group).

Components in the working fluid of an absorption thermal transfer cycle include chemicals which classified according to their use are defined in the art as follows:

“Refrigerant” is the chemical which vaporizes and condenses, or is absorbed, in large volume and the energy associated with this phase change being the essence of the system thermodynamics. In this invention water is the principal refrigerant.

“Absorbent” is the chemical(s) which have relatively low volatilities compared to the refrigerant, and high affinities for the refrigerant. Many suitable absorbents known to the art are suitable for use in this invention, such as those disclosed in U.S. Pat. No. 3,478,530, which is incorporated herein by reference. Lithium, zinc and calcium bromides and chlorides are among suitable absorbents. Lithium bromide compositions are most frequently used in large commercial refrigeration equipment. The properties of the refrigerant and to absorbent(s) together in a refrigerant/absorbent(s) composition define the theoretical limits of the equilibrium thermodynamics of the absorption system. In this invention suitable absorbent(s) are at least one metal salt which is present in an amount sufficient to provide a composition functional as a refrigerant/absorbent(s) composition. Any of the above mentioned salts or combinations of salts, and also salts in combination with other non-interfering absorbents such as glycols or amines are suitable for use in this invention. “Heat and mass transfer additive,” an absorption promoter, serving to accelerate the rate of dissolving or absorption of the refrigerant by the absorbent. Added in small quantities, the heat and mass transfer additive does not directly change the system thermodynamics. Suitable heat and mass transfer additives according to this invention include certain ethers. This invention uses certain ethers as heat and mass transfer additives and not as absorbents. The prior art has used polyfunctional ethers, such as glycol ethers, in significantly large concentrations as absorbents. However, glycol ethers in small quantities, as illustrated by Comparative Example XIV, do not serve as heat and mass transfer additives as intended by the present invention. None of the prior art known to the inventor teaches monofunctional ethers as heat and mass transfer additives. Other additives, as pointed out in the Description of Related Art section above, particularly, the addition of certain amines as described in U.S. Pat. No. 5,419,145, which is incorporated herein in its entirety by reference, known for increasing the rate of absorption of the refrigerant into the absorbent to form the refrigerant/absorbent composition may be used in conjunction with the ether heat and mass transfer additives of this invention, as long as they are non-interfering.

“Corrosion inhibitors” for addition to the working fluid compositions are known to the art, such as, for example, salts of molybdate, nitrate, chromate, etc.; bases such as lithium hydroxide used to raise pH; and organic inhibitors, such as, benzotriazole and related compounds. Corrosion inhibitors sometimes interfere with other additives and one of the advantages of the ether heat and mass transfer additives of this invention is that they are significantly less susceptible to interfering reactions with corrosion inhibitors, and in general are more stable in an absorption chiller environment than other additives known to the prior art.

Other additives, such as, for example, crystallization inhibitors and other absorption promoters may be used as long as they do not interfere with the action of the heat and mass transfer additives of this invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

This invention provides an improved absorption or absorption refrigeration fluid of the type comprising water as the refrigerant and at least one absorbent comprising a metal salt present in an amount sufficient to provide a functional refrigerant/absorbent(s) composition having an amount of monofunctional ether(s) sufficient to provide higher heat and mass transfer resulting in increased rate of thermal transfer of the absorption thermal transfer system.

The metal salt absorbent reduces the vapor pressure of the aqueous refrigerant/absorbent composition sufficiently to provide a composition useful as a refrigerant/absorbent composition. Some suitable salts include at least one cation selected from the group consisting of ammonium, alkali metals, alkaline earth metals, transition metals and mixtures thereof, and at least one anion selected from the group consisting of halide, nitrate, nitrite, thiocyanate and mixtures thereof. Some metal salts useful in this invention include, for example, ammonium or alkali metal, such as lithium, nitrates, nitrites and halides, such as, chlorides, bromides and iodides; alkaline earth metal, such as calcium and magnesium, transition metal, such as iron, cobalt, copper, aluminum and zinc halides and thiocyanates; and mixtures thereof. Particularly suitable for use in this invention are lithium bromide, lithium chloride, lithium iodide, zinc chloride, zinc bromide, zinc iodide, calcium chloride, calcium bromide, calcium iodide, lithium nitrate and mixtures thereof. Particularly suitable combinations include combinations of transition metal or zinc salts, such as zinc bromide, zinc chloride and mixtures thereof, with lithium bromide, lithium chloride and mixtures thereof. Lithium bromide is a particularly useful salt in the refrigerant/absorbent composition of this invention. Suitable initial concentrations of metal salts in the refrigerant/absorbent compositions of this invention are about 30 to about 85 weight percent, and preferably, about 45 to about 75 weight percent.

In accordance with certain preferred embodiments of the invention, absorbents for use in the invention comprise one or more metal halide salts. As will be appreciated, absorption fluid compositions in accordance with the invention may also advantageously include one or more corrosion inhibitors, such as described above, or in the form of one or more metal hydroxides, present in low levels or concentrations. Specific preferred candidates of such metal hydroxide corrosion inhibitors include: lithium hydroxide for those fluids of lithium bromide and lithium hydroxide, zinc hydroxide, or possibly zinc oxide, or some combination thereof for those fluids containing zinc and lithium bromide.

The use of lithium hydroxide and the like to control or assist in controlling corrosion is generally known to those skilled in the art. As will be appreciated, the specific amount used of such corrosion inhibitor can be dependent on various factors such as the presence and amounts of other corrosion inhibitors. In general, the corrosion inhibiting inclusion of lithium hydroxide to a concentrated lithium bromide solution will fall in the range of about 0.002N to about 0.300N lithium hydroxide.

It is to be understood, however, that the broader practice of the invention is not necessarily limited to non-acidic solutions. For example, the ether additives of the invention may, if desired, be employed in conjunction with acidic solutions.

In one embodiment of this invention, a useful refrigerant/absorbent composition comprises the combination of zinc and lithium bromides and a corrosion inhibitor. The combination may have ratios of zinc bromide/lithium bromide of about 3/1 to about 1/3 by weight, particularly suitable ratios being about 1.6 to about 1.9. A suitable source of corrosion inhibitor is lithium hydroxide in an amount of about 0.0005 to about 0.02 gram per gram of total salt.

Suitable monofunctional ethers for use as heat and mass transfer additives for aqueous absorption fluids according to this invention include ethers normally liquid at system operating conditions. Suitable monofunctional ethers include aliphatic and aromatic ethers which do not normally form stable, i.e., irreversible, complexes with the metal salt absorbent in the composition, where irreversible is defined as a complex that remains bound substantially longer than the ligand (water) exchange rate. Particularly, poly ethers based upon short chain glycols, such as those forming 5 to about 8 membered rings with the absorbent cation, are not suitable, as demonstrated by Comparative Example XIV.

Suitable aliphatic monofunctional ethers include straight and branched chain symmetric and asymmetric ethers and cyclic ethers. Cyclic ethers may be especially preferred. Aliphatic ethers for use in the practice of the invention include those having about 4 to about 20 carbon atoms, such as, for example, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, nonadecyl, and eicosyl which may be symmetrical or asymmetrical, branched chain, or cyclic. Cyclic ethers, such as, for example, substituted tetrahydrofurans, are examples of preferred cyclic ethers. Lower molecular weight ethers, 6 carbon atoms and less, are generally not as satisfactory for use because they tend to have too high a volatility, resulting in lower performance at higher concentrations of ether additive. At least partially fluorinated ethers, by which is meant an ether containing one or more fluorine atoms replacing one or more hydrogen atoms in the hydrocarbon, such as fluorinated and perfluorinated cyclic ethers, e.g., perfluoro-2-butyltetrahydrofuran, and fluorinated and perfluorinated ethers having about 8 to about 24 carbon atoms, e.g., perfluoroheptyl ether, perfluorooctyl ether, perfluorononyl ether, perfluorodecyl ether, and the like, may serve to provide good results at lower operating temperatures.

Aromatic monofunctional ethers having about 7 to about 20 carbon atoms are suitable for use in this invention, such as, for example, diphenyl ether, methylphenyl ether (anisole), and dibenzyl ether. Also suitable for use in the practice of the invention are at least partially fluorinated aromatic ethers.

At least partially fluorinated ethers such as the fluorinated and perfluorinated compounds described above, e.g., perfluorinated 2-butyltetrahydrofuran, have been found especially suitable for use as heat and mass transfer additives according to this invention due to their enhancement of thermal stability, such as may be necessary for direct-fired double-effect and triple-effect chillers, especially in mixed lithium-zinc bromide compositions.

The amount of monofunctional ether heat and mass transfer additive needed to obtain maximum results depends upon the combination of the specific heat and mass transfer additive used, the refrigerant/absorbent composition, and the operating conditions. The amount of a specific monofunctional heat and mass transfer additive desired for maximum results can be readily determined by one skilled in the art. Suitable relative amounts of heat and mass transfer additive range from about 5 ppm to about 10,000 ppm, and most preferably about 5 ppm to about 2,000 ppm, where such additive proportions are based on the weight of the total refrigerant/absorbent composition. About 50 ppm to about 500 ppm of the heat and mass transfer additive is preferred in many refrigerant/absorbent compositions. When refrigerant/absorbent compositions having lower volatility are used, less volatile heat and mass transfer additives are needed. Unless a heat and mass transfer additive of sufficiently low volatility is used, suitable upper concentrations of heat and mass transfer additives are about 100 ppm to 500 ppm for hydrocarbon ethers and about 400 ppm to about 2000 ppm for perfluorinated ethers, due to the increase in molecular weight.

The lower molecular weight ethers, 8 carbon atoms and less, such as, anisole or butyl ether, do not do as well when run at high temperatures and absorbent concentrations because they tend to be too volatile. A consequence of excessive heat and mass transfer additive volatility is a drop in performance at higher additive concentrations. Higher molecular weight ethers according to this invention, such as those having about 12 to about 24 carbon atoms, including at least partially fluorinated ethers, such as perfluorooctyl ether, perfluorononyl ether, perfluorodecyl ether, and the like, for example, are especially suitable for use in double-effect machines operating with generator temperatures of about 360° F. and triple-effect machines operating with generator temperatures of about 450° F.

The refrigerant/absorbent compositions of this invention may also include one or more other heat and mass transfer additives, such as amines as taught by U.S. Pat. Nos. 5,577,388 and 5,829,259 and alcohols.

The refrigerant/absorbent compositions comprising ethers for use as heat and mass transfer additives in this invention may also contain one or more additional optional additives, such as, for example organic crystallization inhibitors, usually having an amino or hydroxyl functional group, corrosion inhibitors, or other additives, as long as they do not significantly interfere with the activity of the ether function.

This invention includes a process and apparatus for absorption thermal storage, cooling or refrigeration using the refrigerant/absorbent composition of this invention. Suitable apparatus and process for use of the refrigerant/absorbent composition of this invention includes absorption chillers and refrigeration systems as disclosed in U.S. Pat. Nos. 4,966,007, 5,038,574 and 5,186,009, thermal energy storage systems as disclosed in U.S. Pat. 4,823,864, as well as multiple effect absorption refrigeration systems, for example, double effect and dual loop systems disclosed in U.S. Pat. Nos. 3,266,266 and 4,542,628 and triple effect systems disclosed in U.S. Pat. Nos. 5,335,515 and 5,390,509. The disclosures in the aforesaid patents are incorporated herein in their entirety, including but not limited to the descriptions of the apparatus and systems disclosed therein. Especially preferred are the single and double effect absorption chiller and refrigeration systems which include those systems in which the single or double effect components are a portion of the system, such as a dual loop triple effect system comprising combined single stage loops as disclosed in U.S. Pat. No. 4,732,008.

The following examples are set forth in specific detail for exemplification of the invention and should not be considered to limit the invention in any way.

EXAMPLE I

A series of exemplary runs were made using various ethers as additives to aqueous refrigerant/absorbent compositions by passing the mixture or solution over a heat exchanger surface in a falling film test absorber. The absorber used had a heat transfer tube surface area of about 0.09 square meters, a tube 1 meter long having a 28.6 mm outside diameter. The absorber was operated at an initial solution temperature of 48° C., a vapor pressure of 10.0 mbar, a solution flow of 500 grams/minute, a tube temperature of 30° C. and a dew point of 7° C. Tube temperatures, flow rates and vapor pressures during operation were made by suitable monitors.

Butyl ether, in amounts specified in Table I below, as an additive to an aqueous absorption composition of LiBr—H₂O with 60% salt by weight was passed over the test falling film absorber. The results are shown in Table I wherein: H₂O dT is the increase in water temperature on the inside of the cooling tube, solution flow and absorption taking place on the outside of the tube, a larger number showing more heat has been transferred; dx is the change in solution concentration, a direct measure of mass transfer, a larger number showing more water vapor has been absorbed; Q is the absorber load, the product of the water flow rate H₂O dT and the heat capacity of the water, a larger number showing improvement; and h_(o) is the outside film transfer coefficient, based upon the combination of Q, dx, and the thermal resistivity of the metal tubes and cooling water, a larger number showing improvement. These relationships are well known to the art and are more fully described in U.S. Pat. No. 5,419,145, incorporated herein by reference. The results are shown in Table 1.

TABLE 1 Additive H₂O dT dx Q h_(o) ppm ° C. % Watts W/(m²)(° C.) 0 0.76 1.61 856 1016 0 0.76 1.73 850 1002 0 0.75 1.69 838 963 5 0.93 1.94 1060 1816 5 0.91 1.88 1035 1820 5 1.02 2.53 1154 1637 10 0.97 1.74 1105 2019 10 1.03 2.35 1164 1566 10 1.04 2.16 1183 1626 20 0.88 1.83 1003 1731 20 0.96 2.61 1091 1970 20 1.01 2.54 1151 1589 50 0.69 0.99 782 1345 50 0.80 1.99 903 1561 50 0.88 1.90 994 1740 50 0.89 2.00 1007 1794 50 1.01 2.23 1151 1951 50 1.05 2.35 1192 1954 75 1.07 2.49 1216 2070 75 1.09 2.94 1243 1752 75 1.11 2.78 1261 1714 75 1.11 2.88 1261 1887 75 1.12 2.91 1270 1959 100 0.94 2.25 1053 1852 100 1.00 2.71 1124 1702 100 0.96 2.44 1072 1594 150 1.02 2.61 1142 1957 150 1.02 2.69 1148 1585 150 1.06 2.41 1187 1611

EXAMPLE II

In similar manner as Example I, hexyl ether, in amounts specified in Table 2 below, was added to an aqueous refrigerant/absorbent composition having the same composition as Example I and passed over a falling film absorber under the same conditions as set forth in Example I. The results are shown in Table 2.

TABLE 2 Additive H₂O dT dx Q h_(o) ppm ° C. % Watts W/(m²)(° C.) 0 0.93 2.09 1007 1251 0 0.97 2.09 1053 1297 0 0.97 2.12 1045 1186 5 0.96 2.15 1043 1151 5 0.94 2.31 1022 1184 5 0.95 2.27 1025 1178 10 0.95 2.26 1026 1160 10 0.94 2.18 1022 1180 10 0.95 2.19 1025 1162 20 0.97 2.36 1054 1145 20 1.02 2.50 1107 1273 20 0.98 2.35 1062 1231 20 0.96 2.28 1033 1230 20 0.94 2.26 1023 1223 50 1.10 2.71 1189 1503 50 1.11 2.68 1207 1420 50 1.11 2.61 1201 1426 100 1.14 2.13 1236 2054 100 0.23 2.53 1335 1621 200 1.66 3.49 1795 2704 200 1.41 3.81 1523 1981 500 1.42 3.25 1540 2835 500 1.47 3.24 1586 2784 1000 1.68 3.74 1820 3056 1000 1.59 4.07 1716 2713

EXAMPLE III

In similar manner to Example I, octyl ether, in amounts specified in Table 3 below, was added to an aqueous refrigerant/absorbent composition having the same composition as Example I and passed over a falling film absorber under the same conditions as set forth in Example I. The results are shown in Table 3.

TABLE 3 Additive H₂O dT dx Q h_(o) ppm ° C. % Watts W/(m²)(° C.) 0 0.79 1.94 888 1255 0 0.81 2.32 904 1054 0 0.81 2.48 904 1039 10 0.86 2.27 964 1019 10 0.84 2.56 940 952 10 1.09 2.96 1219 1601 10 1.09 2.99 1227 1602 10 1.09 2.99 1213 1582 20 0.89 2.46 984 1105 20 0.93 2.83 1029 1242 20 1.08 2.95 1198 1496 35 0.93 2.46 1027 1221 35 0.97 2.71 1074 1188 50 0.82 2.26 909 1046 50 0.88 2.56 972 1100 50 0.98 3.32 1090 1226 100 0.93 2.74 1028 1261

EXAMPLE IV

In similar manner to Example I, methyl phenyl ether (anisole), in amounts specified in Table 4 below, was added to an aqueous refrigerant/absorbent composition having the same composition as Example I and passed over a falling film absorber under the same conditions as set forth in Example I. The results are shown in Table 4.

TABLE 4 Additive H₂O dT dx Q h_(o) ppm ° C. % Watts W/(m²)(° C.) 0 0.78 2.10 908 1157 0 0.77 2.14 894 1147 0 0.78 2.19 900 1102 0 0.79 2.16 912 1119 7.6 0.77 2.06 897 1369 7.6 0.78 2.08 902 1322 7.6 0.78 2.12 906 1288 17.1 0.75 1.92 873 1523 17.1 0.78 2.00 906 1510 17.1 0.80 2.09 928 1417 25.8 0.79 2.15 917 1379 25.8 0.80 2.17 933 1351 49.4 0.80 2.04 924 1463 49.4 0.81 2.09 941 1430 49.4 0.81 2.11 941 1407 103.1 0.79 2.00 912 1535 103.1 0.79 2.06 922 1518 103.1 0.80 2.08 929 1507 203.4 0.77 1.97 900 1574 203.4 0.79 2.02 915 1560 203.4 0.80 2.07 934 1525 304.4 0.67 1.61 772 1562 304.4 0.67 1.61 772 1562 304.4 0.73 1.82 849 1609 304.4 0.78 1.97 910 1605 304.4 0.79 2.06 922 1542 304.4 0.82 2.11 948 1514 496.9 0.77 1.92 897 1621 496.9 0.77 1.97 895 1595 496.9 0.79 2.01 914 1553 754.1 0.76 1.80 878 1681

EXAMPLE V

In similar manner as Example I, butyl ether, in amounts specified in Table 5 below, was added to an aqueous refrigerant/absorbent composition of CaBr₂—H₂0 with 58.8% salt by weight and was passed over a falling film absorber operated at an initial refrigerant/absorbent composition temperature of 37° C., vapor pressure of 11.5 mbar, and tube temperature of 28.2° C. The results are shown in Table 5.

TABLE 5 Additive H₂O dT dx Q h_(o) ppm ° C. % Watts W/(m²)(° C.) 0 0.32 0.79 373 1036 0 0.34 0.51 395 1189 0 0.33 0.77 382 1092 0 0.32 0.76 372 1072 10.4 0.38 1.01 445 1370 10.4 0.34 1.01 389 1146 10.4 0.34 1.11 389 1113 20.2 0.38 1.04 446 1318 20.2 0.39 1.06 447 1305 20.2 0.39 1.08 447 1287 41.1 0.37 0.86 430 1422 41.1 0.36 0.95 424 1325 41.1 0.36 0.88 420 1301 70.7 0.28 0.54 325 1124 70.7 0.34 0.65 399 1367 70.7 0.35 0.70 403 1367 100 0.31 0.54 362 1497 100 0.31 0.64 362 1478 100 0.34 0.71 395 1519 100 0.34 0.77 398 1512 150 0.28 0.58 324 1722 150 0.33 0.57 386 1809 150 0.34 0.66 396 1705 200 0.35 0.80 409 1640 200 0.35 0.84 411 1556 200 0.35 0.89 406 1492 249 0.33 0.62 384 1813 249 0.35 0.68 403 1697 249 0.35 0.69 406 1698 497 0.33 0.63 383 1774 497 0.36 0.50 417 1561 497 0.37 0.63 433 1565 1004 0.31 0.56 365 1829 1004 0.33 0.66 389 1557

EXAMPLE VI

In similar manner as Example I, butyl ether, in amounts specified in Table 6 below, was added to an aqueous refrigerant/absorbent composition of ZnBr₂—H₂O with 81.5% salt by weight and was passed over a falling film absorber operated at initial refrigerant/absorbent composition temperature of 48° C., vapor pressure of 10 mbar, and tube temperature of 30° C. The results are shown in Table 6.

TABLE 6 Additive H₂O dT dx Q h_(o) ppm ° C. % Watts W/(m²)(° C.) 0 0.40 0.59 469 820 0 0.39 0.57 452 804 0 0.39 0.64 459 802 0 0.37 0.56 433 728 0 0.37 0.49 430 745 5 0.45 0.95 531 757 5 0.46 1.04 538 726 5 0.46 1.04 545 727 5 0.46 1.04 545 727 10.2 0.54 1.13 626 860 10.2 0.51 1.20 597 826 10.2 0.52 1.20 604 852 10.2 0.53 1.22 619 880 10.2 0.52 1.20 611 862 19.8 0.59 1.44 696 1020 19.8 0.59 1.39 688 1005 19.8 0.56 1.47 659 955 19.8 0.54 1.46 637 922 30.2 0.61 1.56 714 1084 30.2 0.62 1.52 729 1095 30.2 0.62 1.63 729 1097 30.2 0.60 1.59 708 1034 40.2 0.62 1.68 728 1165 40.2 0.61 1.67 721 1082 40.2 0.62 1.49 726 1073 65.1 0.63 1.72 738 1114 65.1 0.65 1.82 759 1186 65.1 0.65 1.71 759 1174 99.8 0.65 1.54 760 1201 99.8 0.66 1.61 769 1241 99.8 0.65 1.67 763 1240 148.9 0.65 1.64 763 1231 148.9 0.65 1.68 768 1244 148.9 0.65 1.49 760 1211 148.9 0.65 1.51 758 1270 254 0.67 1.72 788 1324 254 0.67 1.65 782 1318 254 0.66 1.63 778 1305 254 0.67 1.55 782 1297 501 0.66 1.58 769 1299 501 0.65 1.50 760 1244 501 0.58 1.10 678 1083 501 0.66 1.50 772 1178 501 0.57 1.19 664 1100 501 0.63 1.56 740 1153 501 0.65 1.43 759 1204 501 0.64 1.45 749 1172

EXAMPLE VII

In similar manner as Example VI, phenyl ether, in amounts specified in Table 7 below, was added to an aqueous refrigerant/absorbent composition of ZnBr₂—H₂O with 81.8% salt by weight and passed over a falling film absorber under the same conditions as set forth in Example VI. The results are shown in Table 7.

TABLE 7 Additive H₂O dT dx Q h_(o) ppm ° C. % Watts W/(m²)(° C.) 0 0.42 0.50 452 622 0 0.42 0.51 456 619 0 0.42 0.31 455 652 5 0.43 0.65 465 590 5 0.44 0.70 474 598 10 0.47 0.82 507 611 10 0.47 0.82 507 611 10 0.46 0.86 502 613 20 0.58 1.21 625 753 20 0.59 1.45 639 760 50 0.70 1.51 758 948 50 0.70 1.51 758 948 50 0.70 1.51 761 956 100 0.70 1.59 755 971 100 0.72 1.71 775 993 200 0.62 1.19 669 940 200 0.70 1.40 761 979 500 0.51 1.02 555 663 500 0.51 0.90 547 657 1000 0.46 0.81 494 591 1000 0.45 0.62 492 596 1500 0.46 0.54 493 599 1500 0.45 0.54 490 604

EXAMPLE VIII

In similar manner as Example VI, methyl phenyl ether (anisole), in amounts specified in Table 8 below, was added to an aqueous refrigerant/absorbent composition having the same composition as Example VI and was passed over a falling film absorber operated under the same conditions as in Example VI. The results are shown in Table 8.

TABLE 8 Additive H₂O dT dx Q h_(o) ppm ° C. % Watts W/(m²)(° C.) 0 0.39 0.49 452 935 0 0.39 0.43 456 967 5 0.38 0.42 449 873 5 0.38 0.51 442 857 10.1 0.37 0.51 438 860 10.1 0.37 0.51 439 850 10.1 0.38 0.52 442 848 25.5 0.39 0.53 457 892 25.5 0.38 0.50 447 876 25.5 0.38 0.51 449 875 50 0.38 0.69 449 894 50 0.38 0.72 444 852 50 0.38 0.72 446 856 100 0.38 0.75 442 754 100 0.38 0.76 440 769 100 0.38 0.76 442 766 150 0.37 0.77 436 726 150 0.37 0.79 435 724 150 0.37 0.77 437 728 250 0.38 0.64 447 824 250 0.35 0.63 413 755 250 0.35 0.65 415 751 500 0.26 0.29 303 604 500 0.27 0.30 318 628 745 0.27 0.32 319 762 745 0.28 0.26 327 635 745 0.28 0.26 331 631

EXAMPLE IX

In similar manner as Example I, hexyl ether, in amounts specified in Table 9 below, was added to an aqueous refrigerant/absorbent composition of equal LiBr—ZnBr₂ in H₂O with 87.0% salt by weight and was passed over a falling film absorber operated at initial refrigerant/absorbent composition temperature of 107° C., vapor pressure of 11.5 mbar, and tube temperature of 88° C. The results are shown in Table 9.

TABLE 9 Additive H₂O dT dx Q h_(o) ppm ° C. % Watts W/(m²)(° C.) 0 0.61 0.74 674 718 0 0.62 0.77 690 751 0 0.60 0.80 666 736 0 0.60 0.80 666 736 0 0.60 0.63 667 741 0 0.59 0.91 659 714 0 0.58 0.66 642 711 20 0.58 0.66 645 733 20 0.58 0.68 639 726 50 0.60 0.70 665 754 50 0.61 0.69 673 772 100 0.64 0.74 715 830 100 0.63 0.72 701 820 200 0.69 0.80 761 928 200 0.68 0.79 749 919 200 0.62 0.74 683 776 200 0.62 0.69 684 746 200 0.61 0.67 682 801 400 0.65 0.86 717 905 400 0.63 0.79 702 897 600 0.65 0.76 724 982 600 0.60 0.73 664 802 600 0.62 0.73 666 821 800 0.66 0.85 717 929 800 0.64 0.79 697 889 800 0.63 0.78 687 874 1000 0.67 0.82 721 983 1000 0.66 0.81 718 966

EXAMPLE X

In similar manner as Example IX, octyl ether, in amounts specified in Table 10 below, was added to an aqueous refrigerant/absorbent composition having the same composition as in Example IX except it was 87.1% salt by weight, and was passed over a falling film absorber operated under the same conditions as in Example IX. The results are shown in Table 10.

TABLE 10 Additive H₂O dT dx Q h_(o) ppm ° C. % Watts W/(m²)(° C.) 0 0.55 0.75 615 725 0 0.57 0.73 629 777 0 0.58 0.73 640 799 0 0.58 0.73 648 840 10 0.69 1.03 764 757 10 0.67 1.00 737 730 25 0.81 1.25 897 952 25 0.80 1.23 884 944 25 0.57 0.73 634 612 100 0.90 1.44 1002 1105 100 0.90 1.43 997 1116 200 0.90 1.22 995 1276 200 0.90 1.21 997 1245 300 0.93 1.29 1028 1122 300 0.93 1.33 1027 1129 500 0.91 1.31 1004 1109 500 0.93 1.33 1033 1137 1000 0.77 1.00 854 992 1000 0.82 1.11 904 1013 1000 0.59 0.72 651 1002 1000 0.65 0.97 720 956

EXAMPLE XI

In similar manner to Example IX, methyl phenyl ether (anisole), in amounts specified in Table 11 below, was added to an aqueous refrigerant/absorbent composition having the same composition as Example IX and passed over a falling film absorber under the same conditions as set forth in Example IX. The results are shown in Table 11.

TABLE 11 Additive H₂O dT dx Q h_(o) ppm ° C. % Watts W/(m²)(° C.) 0 0.51 0.66 565 544 0 0.51 0.72 571 546 0 0.52 0.68 575 546 0 0.54 0.84 596 591 0 0.50 0.74 556 556 0 0.53 0.68 591 602 10 0.50 0.70 559 602 10 0.51 0.65 568 630 50 0.36 0.29 403 719 50 0.39 0.24 427 775 100 0.29 0.06 319 628 100 0.29 0.03 320 621 200 0.25 0.07 282 659 200 0.25 0.11 274 591

EXAMPLE XII

In similar manner to Example IX, benzyl ether, in amounts specified in Table 12 below, was added to an aqueous refrigerant/absorbent composition of the same composition as in Example IX except that it was 86.8% salt by weight and a falling film absorber under the same conditions as set forth in Example IX. The results are shown in Table 12.

TABLE 12 Additive H₂O dT dx Q h_(o) ppm ° C. % Watts W/(m²)(° C.) 0 0.61 0.60 679 999 0 0.63 0.50 695 1012 0 0.64 0.65 713 980 0 0.63 0.72 702 967 0 0.62 0.73 692 967 0 0.63 0.73 696 981 20 0.61 0.70 681 973 20 0.62 0.69 686 990 50 0.61 0.66 672 968 50 0.61 0.67 675 975 100 0.59 0.60 653 954 100 0.59 0.59 652 949 200 0.54 0.43 602 1011 200 0.54 0.46 602 1030 200 0.62 0.51 682 882 200 0.62 0.55 683 1208 200 0.62 0.55 684 1249 200 0.62 0.48 693 1271 200 0.63 0.80 693 1049 200 0.63 0.73 696 1060 500 0.57 0.45 631 1121 500 0.57 0.45 635 1186 500 0.58 0.47 642 1148 500 0.57 0.47 634 1124 1000 0.55 0.37 613 934 1000 0.57 0.44 627 986 1000 0.56 0.45 620 993

EXAMPLE XIII

In similar manner to Example IX, perfluoro-2-butyltetrahydrofuran in amounts specified in Table 13 below, was added to an aqueous refrigerant/absorbent composition of the same composition as Example IX except at 73.5% salt by weight and was passed over a falling film absorber operated at an initial refrigerant/absorbent composition temperature of 42° C., vapor pressure of 11.5 mbar, and tube temperature of 30° C. The results are shown in Table 13.

TABLE 13 Additive H₂O dT dx Q h_(o) ppm ° C. % Watts W/(m²)(° C.) 0 0.63 0.38 414 1486 0 0.64 0.39 423 1507 0 0.60 0.31 395 1357 0 0.63 0.32 413 1404 50 1.16 1.07 766 1403 50 1.15 1.08 762 1411 100 1.17 1.07 771 1324 100 1.16 1.09 766 1324 100 1.11 1.15 731 1157 100 0.99 1.11 650 1147 200 0.94 1.15 623 1116 200 0.94 1.14 621 1134 200 0.95 1.14 628 1049 300 0.97 1.18 640 1035 300 0.95 1.18 625 1056 300 0.96 1.15 631 1072 300 0.95 1.16 628 1084 500 1.11 1.02 735 1508 500 1.04 1.19 687 1272 500 1.03 1.16 683 1284 500 1.04 1.16 683 1293 750 1.05 1.17 692 1134 750 0.99 1.05 656 1556 750 1.01 1.17 685 1144 1000 1.03 1.20 681 1263 1000 1.03 1.15 677 1327 1000 0.99 1.17 655 1324 1000 1.00 1.20 661 1334 1500 0.81 0.83 536 2731 1500 0.83 0.81 548 2753

EXAMPLE XIV Comparative Example

In the same manner as Example XIII, perfluoropolyglycolether, in amounts shown in Table 14 below, was added to an aqueous refrigerant/absorbent composition having the same composition as in Example XIII except at 87% salt by weight and was passed over a falling film absorber operated at an initial refrigerant/absorbent temperature of 107° C., vapor pressure of 11.5 mbar, and tube temperature of 88° C. The results are shown in Table 14.

TABLE 14 Additive H₂O dT dx Q h_(o) ppm ° C. % Watts W/(m²)(° C.) 0 0.66 0.66 726 781 0 0.65 0.67 726 759 0 0.65 0.71 722 765 0 0.71 0.58 783 830 0 0.72 0.56 795 879 0 0.65 0.57 721 782 0 0.71 0.69 790 815 10 0.73 0.72 808 883 10 0.73 0.73 809 890 25 0.73 0.74 807 846 25 0.72 0.74 802 844 50 0.69 0.66 763 836 50 0.69 0.66 768 840 100 0.63 0.54 696 757 100 0.63 0.54 697 760 200 0.61 0.36 679 694 200 0.60 0.59 660 716 200 0.61 0.47 673 753 200 0.63 0.52 694 694 500 0.62 0.52 688 771 500 0.63 0.52 693 776 1000 0.57 0.35 627 798 1000 0.56 0.35 623 804

It is to be understood that discussions of theory, such as the discussion of stable complex formation associated with the use of certain ethers, for example, are included to assist in the understanding of the subject invention and are in no way limiting to the invention in its broad application.

While in the foregoing specification this invention has been described in relation to certain preferred embodiments thereof, and many details have been set forth for purpose of illustration it will be apparent to those skilled in the art that the invention is susceptible to additional embodiments and that certain of the details described herein can be varied considerably without departing from the basic to principles of the invention. 

I claim:
 1. An absorption fluid composition comprising aqueous refrigerant, at least one metal halide salt absorbent present in an amount to provide a composition useful as a refrigerant/absorbent and at least one monofunctional ether beat and mass transfer additive normally liquid at system operating conditions and present in an amount effective as an absorption promoter.
 2. An absorption fluid composition according to claim 1 wherein said at least one monofunctional ether heat and mass transfer additive is an aliphatic ether having about 4 to about 20 carbon atoms.
 3. An absorption fluid composition according to claim 2 wherein said at least one monofunctional ether heat and mass transfer additive contains a cyclic ether structure.
 4. An absorption fluid composition according to claim 1 wherein said at least one monofunctional ether heat and mass transfer additive is at least partially fluorinated.
 5. An absorption fluid composition according to claim 4 wherein said at least one monofunctional ether heat and mass transfer additive is an aliphatic fluorinated or perfluorinated ether having about 8 to about 24 carbon atoms.
 6. An absorption fluid composition according to claim 4 wherein said at least one monofunctional ether heat and mass transfer additive comprises at least one substituted perfluorinated tetrahydrofuran.
 7. An absorption fluid composition according to claim 1 wherein said at least one monofunctional ether heat and mass transfer additive is an aromatic ether having about 7 to about 20 carbon atoms.
 8. An absorption fluid composition according to claim 1 having about 5 ppm to about 10,000 ppm of said at least one monofunctional ether heat and mass transfer additive, based upon the weight of the total absorption fluid composition.
 9. An absorption fluid composition according to claim 1 having about 5 ppm to about 2,000 ppm of said at least one monofunctional ether heat and mass transfer additive, based upon the weight of the total absorption fluid composition.
 10. An absorption fluid composition according to claim 1 having about 50 ppm to about 500 ppm of said at least one monofunctional ether heat and mass transfer additive, based upon the weight of the total absorption fluid composition.
 11. An absorption fluid composition according to claim 1 wherein said at least one metal halide salt absorbent is selected from the group consisting of lithium bromide, zinc bromide, calcium bromide and mixtures thereof.
 12. An absorption fluid composition according to claim 1 additionally comprising at least one corrosion inhibitor.
 13. An absorption fluid composition according to claim 12 wherein said corrosion inhibitor comprises a corrosion inhibiting quantity of at least one metal hydroxide. 